I got responses from WealthSimple as below:
We want to assure you that we are aware of this error, and it appears to be affecting a number of our users. Our programming team is actively investigating the root cause and has been in contact with the Canada Revenue Agency (CRA) to resolve this as quickly as possible.
We understand how frustrating this can be, and we want to keep you updated on our progress. We’ll be sure to inform you as soon as we have more information or a resolution.
In the meantime, we strongly advise against making repeated attempts to submit your return while receiving this error. After five failed NETFILE attempts, your NETFILE account may be locked, requiring you to contact the CRA directly to have it unlocked. This limitation applies across all tax software platforms, not just Wealthsimple Tax.
