Something wrong with (my use of) Laravel sync

I have three models:

• clubOffers
• Coupons
• clubOfferCouponPivot (table contains: coupon_id, club_offer_id, and timestamps)

In clubOffer Model:

public function coupons(): BelongsToMany
    {
        return $this->belongsToMany(Coupon::class,'club_offer_coupon_pivot','coupon_id');
    }

In coupon Model:

public function clubOffers(): BelongsToMany
    {
        return $this->belongsToMany(ClubOffer::class, 'club_offer_coupon_pivot','club_offer_id');
    }

In clubOfferCouponPivot Model (I suspect the problem is in here):

protected $table = 'club_offer_coupon_pivot';
public function clubOffers()
    {
        return $this->belongsTo(ClubOffer::class);
    }

    public function coupon()
    {
        return $this->belongsTo(Coupon::class);
    }

    public function coupons()
    {
        return $this->hasManyThrough(Coupon::class,ClubOffer::class);
    }

In my controller, I create a new Coupon model and save it to the database. After that, I want to associate any offers that might exist with it into the pivot table.

When I try to do it from the coupon side of things:

$offers = $clubOffers->where('club_id','=',$cg->id_clubgroup);
foreach ( $offers as $offer ) $coupon->clubOffers()->sync($offer->id);

I get this error: Field 'coupon_id' doesn't have a default value insert into club_offer_coupon_pivot (club_offer_id) values (1) where the value 1 is actually the coupon_id

But when I try to do it from the offer side of things, I get the opposite error:

$offers = $clubOffers->where('club_id','=',$cg->id_clubgroup);
foreach ( $offers as $offer ) $offer->coupons()->sync($coupon->id);

Field 'club_offer_id' doesn't have a default value insert into club_offer_coupon_pivot (coupon_id) values (1213) where the value 1213 is actually the club_offer_id

I have tried all of the following, all come back with varying degrees of failed.

$coupon->clubOffers()->sync($offer->id);
$coupon->clubOffers()->sync($coupon->id,$offers);
$coupon->clubOffers()->sync(['coupon_id'=>$coupon->id],$offers);

and several other variations. Help, please?