Many people aren't aware that you can offer SEIS & EIS to UK investors even if your company is not a UK company.
In order to qualify for SEIS & EIS, a company doesn't need to be incorporated in the UK, but it does need to be registered as a foreign company:
https://www.gov.uk/register-as-an-overseas-company
You'll also need a UK presence, which means either:
you have a fixed place of business in the UK through which the company’s business is wholly or partly carried on; or
an agent acting on behalf of the company has and habitually exercises authority to enter into contracts on behalf of the company.