Paying into a Coutts account - problem

I have a problem trying to pay some money into someone else's Coutts bank account. For 3 years I have been paying an amount into this account 4 times a year from my Co-op account internet banking. Now want to pay from my Barclays account internet banking and trying to set up a funds transfer. The box to put the account number will only takes 8 numbers, the account number I am trying to use is 10 numbers although the last 4 numbers are 0000

I spend hours yesterday on the phone to Barclays trying to sort it out, I spoke to several different people and being told all different things, in the end they told me to call at the branch which I have done this morning, probably to get rid of me, and I have got nowhere. They said the account number must be wrong

I have been using this sort code and account number for 3 years to pay from Co-op successfully

I have checked with the Co-op that these are the numbers they have been using - all OK

I know the other payments have arrived in the account

I have checked with the person I am trying to pay that the numbers are right - all OK

I phoned Coutts to check if their account numbers are 10 digits, I didn't want to give the name or account details or ask them about a specific person's account, just asking generally, but they would not answer anything at all

Someone along the way, can't now remember who, suggested that I knock off two of the four 0000 at the end of the account number to maker it 8 digits but what if the money goes into the wrong account?

Any help would be appreciated I need to get this paid