Yes, its safety when used as a food additive has been approved by the U.S. Food and Drug Administration (FDA), European Food Safety Authority (EFSA),  Joint FAO/WHO Expert Committee on Food Additives (JECFA), as well as other authorities.

FDA

SAPP is generally recognized as safe when used in accordance with good manufacturing practice (2) AND can be used as a color or coloring adjunct, dough strengthener, emulsifier or emulsifier salt, flavoring agent or adjuvant, flour treating agent, formulation aid, leavening agent, oxidizing or reducing agent, and sequestrant in food. (3)

EFSA
Disodium diphosphate (E450i) is listed in Commission Regulation (EU) No 231/2012 as an authorised food additive and categorized as “additives other than colours and sweeteners” (4)

Safety re-evaluation in 2019
In 2019, EFSA considered disodium pyrophosphate to be of low acute oral toxicity and there was no concern with respect to genotoxicity and carcinogenicity.

Also, no effects were reported in developmental toxicity studies. EFSA derived a group acceptable daily intake (ADI) for phosphates expressed as phosphorus of 40 mg/kg body weight (bw) per day and concluded that this ADI is protective for the human population.

Authorised Uses And Use Levels
Its application is listed in diphosphates E450 and the max uses level is 5000 (mg/l or mg/kg as appropriate).

The following foods may contain with it (5):

Processed fish and fishery products
Biscuits and rusks

http://www.chinafooding.com/Sodium_acid_pyrophosphate