Catalyzes the asymmetric hydrolysis of diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) to yield AMP and ATP (By similarity). Exhibits decapping activity towards FAD-capped RNAs and dpCoA-capped RNAs in vitro (PubMed:32432673). H2O + P(1),P(4)-bis(5'-guanosyl) tetraphosphate = GMP + GTP + 2 H(+) a 5'-end CoA-ribonucleoside in mRNA + H2O = (R)-4'-phosphopantetheine + a 5'-end phospho-adenosine-phospho-ribonucleoside in mRNA + 2 H(+) a 5'-end FAD-phospho-ribonucleoside in mRNA + H2O = a 5'-end phospho-adenosine-phospho-ribonucleoside in mRNA + FMN + 2 H(+) Divalent metal ions. Belongs to the Nudix hydrolase family.