Acts 8:16

οὔπω γὰρ ἦν ἐπ᾽ οὐδενὶ αὐτῶν ἐπιπεπτωκός, μόνον δὲ βεβαπτισμένοι ὑπῆρχον εἰς τὸ ὄνομα τοῦ Χριστοῦ Ἰησοῦ.

RBT Greek Interlinear:

Strongs 3764; oudepō; οὐδέπω; Not yet; Adv

Strongs 1063; gar; γὰρ; for; Conj

Strongs 1510; ēn; ἦν; was; V-IIA-3S

Strongs 1909; ep’; ἐπ’; upon; Prep

Strongs 3762; oudeni; οὐδενὶ; nothing; Adj-DMS

Strongs 846; autōn; αὐτῶν; of themselves; PPro-GM3P

Strongs 1968; epipeptōkos; ἐπιπεπτωκός; that which has fallen; V-RPA-NNS

Strongs 3440; monon; μόνον; only; Adv

Strongs 1161; de; δὲ; and; Conj

Strongs 907; bebaptismenoi; βεβαπτισμένοι; those who have been baptized; V-RPM/P-NMP

Strongs 5225; hypērchon; ὑπῆρχον; they were pre-existing; V-IIA-3P

Strongs 1519; eis; εἰς; into; Prep

Strongs 3588; to; τὸ; the; Art-ANS

Strongs 3686; onoma; ὄνομα; name; N-ANS

Strongs 3588; tou; τοῦ; the; Art-GMS

Strongs 2962; kyriou; κυρίου; Master; N-GMS

Strongs 2424; Iēsou; Ἰησοῦ; Salvation; N-GMS

RBT Translation:

ὑπῆρχον εἰς τὸ ὄνομα - Pre-Existing into the Name

For that which has fallen upon, was not yet being on anyone of themselves, and only those who have plunged were pre-existing into the Name of the Master, Salvation.³⁷

Julia Smith Literal 1876 Translation:
(For not yet was it fallen upon any of them: only they were immersed into the name of the Lord Jesus.)

LITV Translation:
For He had not yet fallen on any one of them, but they were only being baptized in the name of the Lord Jesus.

Footnotes

37

Translators appear not to understand ὑπῆρχον "to make beginning/take initiative" and seem to drop it or flatten it out of existence altogether. In Greek, “they have been plunged (baptized) in” would be expressed in the perfect passive (or middle-passive) indicative of βαπτίζω: ἐβαπτίσθησαν ἐν. This is not in the text, but is made up. 

What is written?

βεβαπτισμένοι ὑπῆρχον εἰς

"those who were dipped were taking intiative into"

There is no prepostion ἐν "in" but rather εἰς "into." 

ὑπῆρχον εἰς + acc./dative – Used with an accusative object and εἰς + accusative/dative to indicate proactive or contributive action. For example ὑ. εὐεργεσίας εἴς τινα or τινι is literally, “take the initiative in [doing] kindnesses to someone.” The accusative marks the benefit or service (εὐεργεσίας), and the dative (τινι) marks the recipient. (Demosthenes, 19.280; Aeschines, 2.26) The construction emphasizes intentional action on behalf of another, rather than mere existence of the favor.

(cf. LSJ ὑπάρχω A.4)