A very polite expression of thanks; a formal/earnest way to say 'thank you very much', often used in business or formal contexts.
この度はご来店いただき、誠にありがとうございます。
Thank you very much for visiting us on this occasion.
長年のご支援、誠にありがとうございます。
Thank you very much for your long-standing support.
お忙しいところご協力いただき、誠にありがとうございます。
Thank you very much for your cooperation despite your busy schedule.