I recently had an interview and have had my travel fees reimbursed. I stupidly mistyped my account number by one digit. Is there anything monzo can do their end to transfer to the correct account? I would rather my future employer didn’t know about this silly mishap 
You’ll have to message them in app to ask. 
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I don’t know anything for sure but I would suggest that if the mistyped number corresponds to a real account, there’s no way Monzo can get involved in diverting funds on the basis of a third party’s say-so.
Under those circumstances you’d need to go to the sender to sort it out, I suggest.
If the account number isn’t valid, then I’m not sure what happens but, again, I’d be surprised if Monzo can accept the word of a third party as to the routing of funds from an external account.
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I’ve discovered the account number isn’t valid so I assume it will bounce back. I have emailed my future employer to tell them the mistake. Very embarrassing but hopefully all will work out.
Yeah, it’s an embarrassment to have to handle but I think it’s the only way around it. I hope it’s not too painful an experience.
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Do banks not provision account numbers sequentially? I didn’t see any downside to this and since they use base ten also it didn’t seem likely there are enough spare number to do much different.
If so how is it done? Randomly within the number-space? Or in a non-predictable but generally ascending way>
Like card numbers, account numbers are randomly assigned within a set of validity rules.
If you want to read far too much detail about how to determine if a UK account number and sort code combination is valid, search Vocalink modulus checking and you’ll find documents including details on the algorithm and some older versions of the weighting tables used to calculate valid account numbers. 
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Oh it’s just modulus checked? I see the point in other use cases but why with account numbers?
There’s no such thing as too much detail 
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I think the OP is a pretty good example of why. One digit wrong has resulted in an invalid combination, bouncing the payment back, as compared to paying the wrong person, which is on balance a better thing
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That only works if you’re using a small fraction of the number space.
What would you recommend instead?
I’m not recommend any alternative, I’m just saying it would be ideal to have a lot more more than 10^8 possibilities.Obviously card numbers being randomly allocated works a lot better as there are 10^(16-6-1) = 10^ possibilities.
Well, it’s not Card Manufacturing Facts but it’s close enough
Do the Modulus rules for each sort-code get set up to ensure there’s a roughly equal number of accounts per sort code? I imagine if you’d follow the same rule set always some sort-codes would have less valid possibilities than others?
A quick play in excel on some random numbers suggests about 1 in 8 account numbers are valid - so once you get to about 12 million accounts, you’ll need to get a new Sort Code?
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I’m afraid you’ll either have to take the loss, or ask your employer to let their bank know so they can submit a Credit Payment Recovery request to us 
We’ll then be able to send the money back to them and they will be able to send it to your correct details 
The main question here is why the bank allowed them to send the payment to a Vocalink-invalid number. The whole point of modulus checking with things like this (and with 16 digit card numbers) is to catch the errors before they get sent!
Would an off by one error necessarily render the entire account number invalid? (Given we don’t know which digit was typo’d)
I can’t find any documentation for the algorithm but unless they are only using 10% of the number-space (unimaginable) then no. Don’t forget the modulus validation includes the sort code too.
My point was this was shown to be invalid (note the difference between non-existent) and thus it’s being returned. No system should allow sending to an invalid account number as that’s its sole purpose.
Ah you’re correct - I misread that
In which case your point is entirely valid!
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