Add New record action stopped working all of a sudden, not sure what is causing the error

Question

Yesterday afternoon, the Add New record action on 3 different interfaces stopped working and the process models show the same following error: 
 
 The only change that was made to those 3 interfaces was the following highlighted section was added into the expression mode: 
 
 *Note - after this change was made to the example above I was able to create a new record in that table with no issue, then proceeded to make the change to the other 2 now having issue. Also, we tried putting it back the way it was and it still gave the error so we are stumped as to what is causing this issue now.

Sanchit Gupta (Xebia) · Answer

But you need to understand the root cause of this error is that you are trying to insert an entry in the PLSM_document table with a misMattersMainId that is not present in the PLSM_miscMattersMain table. Since you have configured a Foreign key constraint in PLSM_document table on misMattersMainId column with the permission to restrict any entry in which value of foreign key i.e., misMattersMainId is anything which is not present in the PLSM_miscMattersMain's misMattersMainId (primary key). 
 Now, you need to check in your Add document action that how you are setting up misMattersMainId for the new documents. According to me this action should not be in the PLSM document recordType at first place but instead should be added as a related action in PLSM miscMatterMain recordType so that you can setup the value for foreign key column in the new document added by using the record identifier of the record you are adding this document to.