Postcode invalid, can't register

I am a newbie here and just tried adding my new PV array with my postcode in the UK and I get “The UK postal district ‘BB18 6LF’ is invalid, expecting ‘AANN’, ‘ANN’ or ‘AN’ format e.g. LU7, EH33 or SL1”

I tried without the space but the same message. The postcode hasn’t changed for over 23 years !!
Please would you fix it for me?

It needs just the postal district “BB18” rather than the full postcode