Same issues for me! I received these two messages from Plastiq support. I had some payments go through on 2/13 and on 2/19 they didn't work for me.

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Hi,

We do apologize for any current issues you are having when trying to process payments with Mastercards issued from METABANK or PATHWAY bank. Our team is looking into this issue and we will reach back out as soon as this has been resolved.

Thank you for your understanding and patience.

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Hello,

Please contact your card issuer directly to ensure there are no blocks in place using the card with 3rd party payer companies like Plastiq.

If you are still unable to use the card on payments after confirming with your card issuer, you will need to use a different card for payment. Sorry for the inconvenience.

If you have any other questions please reach out we are happy to help.