I'm currently developing a broker plugin for IG.
When testing my broker buy function for the first time, I ran into the issue of getting a "Balance limit exceeded" message, which I realise means that I've exceeded the $7000 limit on my free Zorro version.

The problem is that my account is not in USD, it's in SEK, so I really only have something like $1100 on this account.

Should I just convert the account currency to dollar, or does it need to be a dollar account?

For the 7000 limit a $ account is assumed. For other currencies the limit can be smaller since only the amount is checked, not the account currency.