Hello @MCC-MarCom ,
Based on that error code seems like the lists aren't syncing correctly, but we as Constant Contact wouldn't be able support any further troubleshooting unfortunately. The integration that you are using is developed by WordPress. Constant Contact support agents are not trained on WordPress’s product. You will need to contact Word Press for further assistance with this error.
However, this WPForms help document I found may be useful for that error code you are receiving, I have attached a link to it here for you.
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