Self-employed

I am having problems entering the GST number for hotels to claim the Ontario Staycation Tax Credit.  I type in the GST number, it contains a combination of letters and numbers and your program will not accept the letters.  I get the message "Please enter a numeric value rounded to the nearest whole number".  In order to save and continue, for the interim, I replaced the letters with zeros.  However I will need to correct before sending to CRA.  Any suggestions?