Generally speaking, since 2006 (at least) such an agreement is required before US companies can sell a foreign country [C4ISR] equipment with certain intel interoperability features.
C22.214.171.124. Bilateral INFOSEC Agreement Signature. The bilateral agreement (e.g.,
CISMOA or COMSEC MOU, INFOSEC Equipment Agreement) must be in place in order for a
purchaser to receive INFOSEC products or services associated with a C4ISR system.
The list of products covered is pretty broad, including anything containing cryptography for instance, which nowadays is pretty much any non-trivial military equipment.
While I'm not entirely certain about this and public details are scant, the lapsing of the agreement probably had something to do with the more anti-US stance of the previous Pakistani (Khan) government. One article notes that the renewal came shortly after the US approved $450 million sale in F-16 parts to Pakistan in late 2022.
The Pakistani government didn't seem too keen to answer press questions about this:
[...] there was no official announcement from either side about the signing of the CIS-MOA. Federal Minister for Information Marriyum Aurangzeb was approached but she did not respond till the filing of this report.