Selling the ChatGPT API on Facebook is possible, but you'll need to ensure that your ad content complies with Facebook's advertising policies, especially regarding the promotion of APIs, software services, and related products. Facebook has strict guidelines around claims and privacy, so your ads should clearly describe the service and avoid any misleading or exaggerated claims. Make sure that the landing page or website you're linking to is fully transparent about what the API does, its pricing, and any potential limitations.
For advertising costs, the lowest-cost option typically involves setting a small daily budget and optimizing for cost-efficient objectives like Lead Generation or Link Clicks. However, keep in mind that Facebook ads still require a budget that aligns with your goals. The cost can vary depending on the competition in your niche and the target audience you're reaching.
If you don't have a physical credit card, you might be able to use a virtual card or PayPal to fund your ads. Alternatively, you can try buying a Facebook ad account from a trusted provider, but be cautious about the legitimacy of third-party purchases. Always make sure that the ad account you're using is compliant with Facebook’s rules to avoid getting restricted or banned.