"b2b" or "B2B" or "b-2-b" or ....

0Hello,02br
02br
00does anyone know if there is a specific rule on how to write the "business-to-business" abbreviation?02br
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00Should I write it in lowercase, uppercase, with hyphens or ???02br
00b2b / B2B / b-2-b02br
02br
00Thanks in advance02br
00Ludo0-