To purchase and Outbacker policy you must be a UK Resident. If you spent more than 183 days in the last year in the UK you are always considered a resident of the UK, if you've spent less then residency is a complicated matter, we are not able to provide guidance on this matter.
We can however provide you the following link which explains in some detail what the rules are for residency https://www.bdo.co.uk/en-gb/insights/tax/private-client/leaving-the-uk . If you are still unclear if you are still a UK resident after reviewing this link then you'll need to query this with a relevant professional. If you confirm to us that you believe you are a UK resident after reviewing this page and as long as you meet our other criteria, we'll be able to issue you a policy.