I have my husband's ID number, but it says that it isn't found when I try to link him

@Emily Joy Kjar Now that's a good question…. Since you both have separate accounts, you can't find him [he is living] and he can't find you [also living]. I guess one way to tackle this to decide which one of you will be the 'lead'.

Let's assume it will be you,. Take your account and create your husband [if you haven't already] and establish him as your spouse. He will have a unique PID tied to your 'living' husband as shown attached to you as viewed from your account. For 'future-proofing' it might not be a bad idea for him to 'create' you in his account.

Now using his account find the logical point where you can connect your husband and his parental/family lines.as shown in your account to those as shown in his account. You will need to create 'duplicates' for those living family members shown in his account in your account [assuming they don't already exist]. Just keep going creating his family line[s] in your account until you can tie into the right spot[s] for his deceased ancestors/relatives at which point you're done

The duplicate/living individuals between your two accounts will have to be left to future generations to 'fix'

I have to ask myself though how does this really 'help'. Any living relatives now existing in his account will not appear in yours unless you create them. Beyond that you and he can each 'see' your respective deceased relatives.

Maybe there's an easier way thru some sort of account sharing, but I don't know…

To flesh out what @Mark McKenzie_1 is saying, all Living entries in FS are unique and only viewable by the login that created them. Only Deceased entries are common to the whole of the Family Tree and are viewable/editable by all. Here's a great article explaining exactly what you're asking about.

https://www.familysearch.org/en/blog/how-to-connect-to-a-family-members-tree