Immigration asking letter guarantee

From my personal experience and research, they want a notarized guarantee from your embassy stating you've never been married.

or divorce decree from previous marriage...

Maybe contract for marriage from embassy you should have been notified of that, maybe guarantee of funds to live in the Philippines

Thank you for everyone's ideas they sent me some idea on the messenger helpline:
Guarantee letter from the petitioner stating your intention to stay here long term as a law-abiding citizen, etc.

[Post under review]

When I was trying to get married in the Philippines I had to go to the American Consulate in Cebu to get a document where I swore under oath that I am not currently married and we both had to get Certificates of No Marriage from the Philippine government.  But we didn't have time to get married while I was there, so we actually got married later in the U.S.  Then, to get my 13a probationary visa I had to apply for a Philippine "Report of Marriage" first.  I did this at the Philippine Embassy Consulate in Washington, D.C.  It took me three visits to the Embassy to complete all documents for my 13a.  Good thing I only lived 55 miles away.  Now it will lapse before I can return to the Philippines and I'll have to start all over with a new 13a application.  Probably my Report of Marriage is still valid.

You already have the signed marriage certificate so the need to prove you do not have marriage of convenience, you do that with something that says you have lived together as husband and wife, location, that you can and will financially support the love of your life and any children for as long as you both shall live and provide for her if you precede her in death, notarized:

Lem

Unfortunately, the US Embassy and Consulates are not currently doing any notary services.  I just emailed the Embassy this week and the answer was "not now".  There was no estimated time for them to resume the services.
I think you have to ask BI exactly what they want.  Maybe it could be a simple notarization available all over the Philippines or something that could be aposilated.  I had to do the latter for my SRRV paperwork.