I'm also having trouble adding my BMO account to Paypal because of this 4-digit transit number.
I tried following the directions that were posted here, but they don't seem to be working. I tried adding 3 (for Newfoundland) to the end of my transit number but it came back invalid. In fact, the only number that didn't come back invalid was 1. I don't know how long it takes those deposits to show up but it's been almost a day now so I don't think it worked.
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