Learn Hardcore German: Leider war der Handy-Empfang im Laden so schlecht, dass ich nicht bezahlen konnte. - Unfortunately the phone reception in the shop was so bad that I could not pay.

In German everyday speech, Handy is the most common loanword for a mobile/cell phone. Although it looks English, native English speakers generally don’t use “handy” to mean “cell phone.” German also has the more formal Mobiltelefon, but Handy is far more frequent in casual contexts.

Why do we say der Handy-Empfang? Why is the article der?

In German compounds, the gender (der/die/das) is determined by the final noun. Here, Empfang (“reception”) is masculine, so the whole compound Handy-Empfang takes der.

Is the hyphen in Handy-Empfang mandatory? Could it be written another way?

Hyphens in German compounds are optional aids for clarity or style, especially when one part is a foreign word. You could also write Handyempfang as one word, which is fully correct by Duden rules. The hyphen simply makes it easier to parse at a glance.

Why is im Laden used instead of in dem Laden?

im is a contraction of in + dem (dative masculine/neuter). Since Laden (“store”) is masculine (der Laden), and the preposition in here requires the dative case (“where?”), we say im Laden instead of the separate words in dem Laden.

What’s going on with the word order: Leider war der Handy-Empfang…?

Starting with Leider (an adverb) puts it in the first position, so German uses verb–subject inversion:
Position 1: Leider
Position 2: war (the finite verb)
Then the subject: der Handy-Empfang.
This is a normal pattern whenever you begin a sentence with something other than the subject.

Why is there a dass clause (…so schlecht, dass ich nicht bezahlen konnte) and why does konnte go to the very end?

dass is a subordinating conjunction introducing a dependent clause with its own subject. In German subordinate clauses, the finite verb moves to the end of the clause. Here you have a modal construction, so the infinitive bezahlen comes just before the finite konnte:
“…so schlecht, dass ich nicht bezahlen konnte.”

What is the difference between zahlen and bezahlen in German?

bezahlen is transitive: it always takes an object (you pay something).
zahlen can be intransitive (“to pay” in general) or transitive (“to pay someone/something”).
In this sentence, bezahlen is used because you’re paying for a purchase (direct object implied).

Could you rephrase the sentence in the perfect tense (present perfect)?

Yes. In conversational German you might say:
Leider ist der Handy-Empfang im Laden so schlecht gewesen, dass ich nicht bezahlen konnte.
Here ist gewesen is the perfect of war, and the subordinate clause stays the same.