My client’s website uses Woo-Square payment gateway to connect with their Square account to accept credit card payments online. Since March '23, they have had an increasing percentage of orders failing for retrieveCustomer errors on CustomerID. For the last several weeks, every card payment fails.
Some customers have a CustomerID in the website database that is different than the CustomerID shown in the Square Transactions report. Before while some card payments were still succeeding, I saw that sometimes customers with two different CustomerIDs had card payments succeed and some had card payments fail every time. Customers with the same CustomerID in both the website and Square always had successful card payments.
Any ideas would help, but the website code is not custom, it is all in Wordpress plugins, so any fix would have to be at the level of plugin settings, data values, etc. or info about WooCommerce-Square gateway issues and fixes for this.
Although Square integrates with WooCommerce to process payments, the integration is operated and managed by WooCommerce. For help with WooCommerce-specific questions, you’ll need to submit a ticket with their Support team.
The WooCommerce Customer Support team will be able to help you with all Square integration related questions. 
I agree that you can’t support the Woo part. Can you tell me why Square would start using a different CustomerID for our customers than the ones they have had for two years or more? If Square changes a CustomerID, does it report that to us somehow?
Thank you,
Kathy
When duplicate customer profiles are identified and merged, either manually by the seller or using automated detection, the existing profiles are merged into a single profile that is assigned a new ID.
If you specify the ID of a customer profile that was deleted in a merge operation, the Customers API returns the new customer profile. For example, suppose customers A and B are merged and a new customer C is created. If you call RetrieveCustomer using the ID of customer A or B, the Customers API returns customer C.
Very clear!
Upon interrogation, my clients admitted that they might have switched Square accounts around the time payments stopped working. They are an artists’ guild and had no tech help at the time.
Thank you very much,
Kathy