Tenants with non-UK phone number

I can perhaps understand that landlord needs to have a UK phone number (although their reason for this is unjustifiable) but why create this chick-and-egg paradox for overseas tenants when you are supposed to ease the letting industry?

A prospective tenant from US has accepted the property for work but we are both stuck at Rent Now’s first step of requesting holding deposit because he does not have a UK phone number, therefore I as landlord cannot access any tenancy creation tools such as referencing, or AST drafting and there is not other way to access these paid services individually despite having paid for the whole Rent Now package.

It is not a legal requirement for tenants to have a UK phone number, and I think OpenRent may be effectively blocking a large chunk of customer base especially in markets like London.