'Sapta' (seven) refers to svaras, not a seven-śruti saṁvāda interval; Mātaṅga does not accept seven-śruti saṁvāda beyond nine and thirteen.
Body (pseudocode)
SAMVADA_INTERVALS = {9,13} # 7 is rejected; arises from a punctuation misreading
Inputs / output
→ samvada_intervals_allowed
Evidence (1)
p. vol_I_p077 · #2832« P.t. combines sapta-svarāķ etc. and that has led to a misunderstanding among scholars to the effect that Matanga has accepted the 'samvāda' of seven- sruti interval »