IRS number on the U.S. Customs Invoice

My company is on BPCS 5.1 which we century-dated ourselves.

My company acquired a Canadian Company late last year, and we are in the
final stages of the project to convert this company to our IT systems.
I am currently programming an application which will generate a document
known as the "U.S. Customs Invoice" which has to be presented at the
U.S. border for shipments going from Canada to the U.S.

For the buyer and ship-to entities on the header portion of this
document, we have to print what is known as the "I.R.S. Number." After
doing some research I believe this is the reference number formally
known as the "Employer Identification Number" (E.I.N.). You can think
of this as the social security number for businesses; it is the
identification number issued to businesses by the I.R.S.

My question is, is there a data element in native BPCS to store this
number? When I look in RCM, I see a field named CTXID (description, Tax
ID Number). In BPCS, this is an alphanumeric field of length 12. The
E.I.N. is a 9-digit number in the format of 99-9999999. Would it be
appropriate to store the customer's EIN in field CTXID? Thanks.

Best regards,
Bob Hermann