Add clarifying notes around using round number for TEMPLATE (and MULTIPLE) product orders

Author: wjdp

features/merchant-selection-template.mdx

@@ -35,6 +35,7 @@ Templates you create yourself cannot be used in the Playground environment. Inst
 
         - Set the `type` of the `products` object to `TEMPLATE`
         - Set the `template_id` in the `products` object to the ID you have obtained from the previous step.
+        - Ensure the `face_value` is a round number and equal or greater than the minimum face value of the products selected.
 
         ```json Request example {9-12}
         {

reference/2024-02-05/openapi.json

@@ -1249,7 +1249,7 @@
         "properties": {
           "face_value": {
             "title": "Face Value",
-            "description": "Face value of the payout link. The currency of the face value is inferred from the product selection.",
+            "description": "Face value of the payout link. The currency of the face value is inferred from the product selection.\n\nWhat value is allowed depends on the product mode:\n- When ordering a `SINGLE` product this field follows the allowed values from the selected product.\n- If using `MULTIPLE` or `TEMPLATE` this value must be: equal or greater than the minimum face value of the products selected and be a round number.",
             "minimum": 0.01,
             "example": 10,
             "type": "number"