If you haven't got C, either build the missing parts (assuming that the customer is the right one) [0], or find another customer [1].
If you realise they don't really need B that much, then no amount of sales is going to help you [2]. Time to pivot based on A or find a new B?
[0] Chasm crossing - A Pennarun, https://archive.is/cHeKx
[1] Users you don't want - M Seibel, https://archive.is/tCCLa
[2] Making something people want - T Blomfield, https://archive.is/8IDcl
If you haven't got C, either build the missing parts (assuming that the customer is the right one) [0], or find another customer [1].
If you realise they don't really need B that much, then no amount of sales is going to help you [2]. Time to pivot based on A or find a new B?
[0] Chasm crossing - A Pennarun, https://archive.is/cHeKx
[1] Users you don't want - M Seibel, https://archive.is/tCCLa
[2] Making something people want - T Blomfield, https://archive.is/8IDcl