There is an issue here:
https://github.com/likecoin/iscn-js/blame/19f0dd3ec9f6a4b12020e7bc70b3e6297f035275/src/messages/authz.ts#L175
The type set in formatMsgGrantGenericAuthorization is number.
Because of this mismatch this line will get:
TypeError: expiration.toNumber is not a function