Obtaining a K1 fiance visa for your boyfriend or girlfriend to come to the US requires the filing of several documents both here in the United States and at a consular post abroad. Further, the couple must meet minimum eligibility criteria such as being able and intending to marry.
One requirement that often causes problems for spouses who would otherwise qualify for the K1 fiancee visa is having a sponsor. With few exceptions, every foreign national that lives in the United States on a family-based immigrant visa must have a sponsor. Generally, USCIS requires the sponsor to submit form I-864 and show that he or she has income at or above 125% of the federal poverty level for the number of people in the household, including the immigrant.
Sponsorship requirements for a K1 visa applicant are usually less stringent, because once he or she adjusts status in the United States, they will need a regular I-864 sponsor. Most US consulates abroad require the K1 sponsor to have income at just 100% of the federal poverty level and to submit form I-134, not form I-864.