diff --git a/api/v3/Mjwpayment.php b/api/v3/Mjwpayment.php
index 0b1421e66617d7bb97516ae10d50b569a9325987..8b297983dde79da2d6391af5ffcd649a43f690c1 100644
--- a/api/v3/Mjwpayment.php
+++ b/api/v3/Mjwpayment.php
@@ -9,10 +9,11 @@
 
 /**
  * @todo mjwpayment.get_contribution is a replacement for Contribution.get
- *   mjwpayment.get_payment is a replacement for Payment.get
  *   which support querying by contribution/payment trxn_id per https://github.com/civicrm/civicrm-core/pull/14748
  *   - These API functions should be REMOVED once core has the above PR merged and we increment the min version for the extension.
  *   - The change is small, but to re-implement them here we have to copy quite a lot over.
+ * @todo mjwpayment.get_payment is a replacement for Payment.get:
+ *   https://github.com/civicrm/civicrm-core/pull/16603
  */
 /**
  * Adjust Metadata for Get action.
@@ -132,22 +133,39 @@ function _civicrm_api3_mjwpayment_contribution_add_supported_fields(&$contributi
 function _civicrm_api3_mjwpayment_get_payment_spec(&$params) {
   $params = [
     'contribution_id' => [
-      'title' => 'Contribution ID',
+      'title' => ts('Contribution ID'),
       'type' => CRM_Utils_Type::T_INT,
     ],
     'entity_table' => [
-      'title' => 'Entity Table',
+      'title' => ts('Entity Table'),
       'api.default' => 'civicrm_contribution',
     ],
     'entity_id' => [
-      'title' => 'Entity ID',
+      'title' => ts('Entity ID'),
       'type' => CRM_Utils_Type::T_INT,
       'api.aliases' => ['contribution_id'],
     ],
     'trxn_id' => [
-      'title' => 'Transaction ID',
+      'title' => ts('Transaction ID'),
+      'description' => ts('Transaction id supplied by external processor. This may not be unique.'),
       'type' => CRM_Utils_Type::T_STRING,
     ],
+    'trxn_date' => [
+      'title' => ts('Payment Date'),
+      'type' => CRM_Utils_Type::T_TIMESTAMP,
+    ],
+    'financial_trxn_id' => [
+      'title' => ts('Payment ID'),
+      'description' => ts('The ID of the record in civicrm_financial_trxn'),
+      'type' => CRM_Utils_Type::T_INT,
+      'api.aliases' => ['payment_id', 'id'],
+    ],
+    'is_payment' => [
+      'title' => ts('Is Payment'),
+      'description' => ts('Is this entry a payment (is_payment=1) or a reversal of a payment (is_payment=0)?'),
+      'type' => CRM_Utils_Type::T_BOOLEAN,
+      'api.default' => TRUE,
+    ],
   ];
 }
 
@@ -162,49 +180,56 @@ function _civicrm_api3_mjwpayment_get_payment_spec(&$params) {
  * @throws \CiviCRM_API3_Exception
  */
 function civicrm_api3_mjwpayment_get_payment($params) {
-  $financialTrxn = [];
-  $limit = '';
-  if (isset($params['options']) && CRM_Utils_Array::value('limit', $params['options'])) {
-    $limit = CRM_Utils_Array::value('limit', $params['options']);
-  }
-  $params['options']['limit'] = 0;
-
-  $ftParams['is_payment'] = 1;
-  if ($limit) {
-    $ftParams['options']['limit'] = $limit;
-  }
+  $ftParams = [];
 
-  if (!empty($params['trxn_id'])) {
-    $ftParams['trxn_id'] = $params['trxn_id'];
-    $financialTrxn = civicrm_api3('FinancialTrxn', 'get', $ftParams);
-    if (!empty($financialTrxn['count'])) {
-      $financialTrxnIDs = CRM_Utils_Array::collect('id', CRM_Utils_Array::value('values', $financialTrxn));
-      $params['financial_trxn_id'] = ['IN' => $financialTrxnIDs];
-      $eft = civicrm_api3('EntityFinancialTrxn', 'get', $params);
-      foreach ($eft['values'] as $eftID => $eftValues) {
-        $financialTrxn['values'][$eftValues['financial_trxn_id']]['contribution_id'] = $eftValues['entity_id'];
+  // To get by contribution ID we need to "join" civicrm_financial_trxn.id on civicrm_entity_financial_trxn.financial_trxn_id
+  // But this is a pseudo API so we can't do that directly (FinancialTrxn can).
+  if (isset($params['entity_id']) && ($params['entity_table'] === 'civicrm_contribution')) {
+    $eftParams = [
+      'entity_id' => $params['entity_id'],
+      'entity_table' => $params['entity_table'],
+      'options' => ['limit' => 0],
+    ];
+    $eft = civicrm_api3('EntityFinancialTrxn', 'get', $eftParams)['values'];
+    $eftIds = [];
+    foreach ($eft as $efts) {
+      if (empty($efts['financial_trxn_id'])) {
+        continue;
       }
+      $eftIds[] = $efts['financial_trxn_id'];
+      $map[$efts['financial_trxn_id']] = $efts['entity_id'];
+    }
+    if (!empty($eftIds)) {
+      $ftParams = [
+        'id' => ['IN' => $eftIds],
+        'is_payment' => $params['is_payment'],
+      ];
     }
   }
-  else {
-    $eft = civicrm_api3('EntityFinancialTrxn', 'get', $params);
-    if (!empty($eft['values'])) {
-      $eftIds = [];
-      foreach ($eft['values'] as $efts) {
-        if (empty($efts['financial_trxn_id'])) {
-          continue;
-        }
-        $eftIds[] = $efts['financial_trxn_id'];
-        $map[$efts['financial_trxn_id']] = $efts['entity_id'];
-      }
-      if (!empty($eftIds)) {
-        $ftParams['id'] = ['IN' => $eftIds];
-        $financialTrxn = civicrm_api3('FinancialTrxn', 'get', $ftParams);
-        foreach ($financialTrxn['values'] as &$values) {
-          $values['contribution_id'] = $map[$values['id']];
-        }
+
+  // If we have IDs from EntityFinancialTrxn merge them here.
+  $ftParams = array_merge($params, $ftParams);
+  $ftParams['return'] = array_values(CRM_Utils_Array::collect('name', civicrm_api3('FinancialTrxn', 'getfields')['values']));
+  $ftParams['return'][] = 'id.entity_id';
+  $ftParams['sequential'] = 0;
+  $financialTrxn = civicrm_api3('FinancialTrxn', 'get', $ftParams)['values'];
+  if (empty($eftIds) && !empty($financialTrxn)) {
+    $eftParams = [
+      'financial_trxn_id' => ['IN' => array_keys($financialTrxn)],
+      'entity_table' => 'civicrm_contribution',
+    ];
+    $eft = civicrm_api3('EntityFinancialTrxn', 'get', $eftParams)['values'];
+    foreach ($eft as $efts) {
+      if (empty($efts['financial_trxn_id'])) {
+        continue;
       }
+      $map[$efts['financial_trxn_id']] = $efts['entity_id'];
     }
   }
-  return civicrm_api3_create_success(CRM_Utils_Array::value('values', $financialTrxn, []), $params, 'Payment', 'get');
+  // Map contribution_id from id.entity_id
+  foreach ($financialTrxn as &$values) {
+    $values['contribution_id'] = $map[$values['id']] ?? NULL;
+  }
+
+  return civicrm_api3_create_success($financialTrxn ?? [], $params, 'Mjwpayment', 'get_payment');
 }